Hydrogen storage alloys, method for producing the same, and anodes for nickel-hydrogen rechargeable battery

ABSTRACT

The present invention relates to hydrogen storage alloys, methods for producing the same, and anodes produced with such alloys for nickel-hydrogen rechargeable batteries. The alloys are useful as electrode materials for nickel-hydrogen rechargeable batteries, excellent, when used as anode materials, in corrosion resistance or activity such as initial activity and high rate discharge performance, of low cost compared to the conventional alloys with a higher Co content, and recyclable. The alloys are of a composition represented by the formula (1) and has a substantially single phase structure, and the crystals thereof have an average long axis diameter of 30 to 160 μm, or not smaller than 5 μm and smaller than 30 μm. The present anodes for rechargeable batteries contain at least one of these hydrogen storage alloys. 
 
RNi x Co y M z    ( 1 ) 
(R: rare earth elements etc., M: Mg, Al, etc., 3.7≦x≦5.3, 0.1≦y≦0.5, 0.1≦z≦1.0, 5.1≦x+y+z≦5.5)

FIELD OF ART

The present invention relates to hydrogen storage alloys, methods forproducing the same, and anodes for nickel-hydrogen rechargeablebatteries, which alloys are useful as electrode materials fornickel-hydrogen rechargeable batteries, and when used as the electrodematerials, exhibit particularly excellent cycle life characteristics.

Background Art

Metal oxide-hydrogen batteries with a hydrogen anode made of a hydrogenstorage alloy have recently been attracting attention for theirinherently high energy density, advantageous volume efficiency, safeoperability, and excellence in both performance and reliability. In thistype of batteries, AB₅ type hydrogen storage alloys are mainly used asthe anode material. For improved battery performance, the alloys aredemanded to have various properties, such as hydrogen storage capacity,equilibrium pressure, corrosion resistance, and flatness of the plateau.Some of these properties are conflicting with each other, so thatstudies have been made for improving one property without sacrificingthe other, some with practical success.

For improving the corrosion resistance of hydrogen storage alloys, whichwill contribute to improved battery cycle life, addition of cobalt (Co)to the alloys has been observed to give certain effects and put intopractice. However, since Co is very expensive, the addition thereofdisadvantageously increases the alloy cost. Thus studies have been madeto retain the corrosion resistance of an alloy even at a reduced Cocontent. Various solutions have been attempted for this purpose, such asusing other additional elements with Co, increasing the ratio of theB-site components mainly consisting of Ni to the A-site componentsmainly consisting of rare earth elements, and the combination of these.

In the above methods, retention of the corrosion resistance at a reducedCo content is achieved. However, is another problem arises in the methodof using other additional elements, that the increased number ofcompositional elements of the alloy makes recycling of the usedbatteries difficult, which increases the costs for recycling. In themethod of increasing the ratio of the B-site components, homogenizationof the alloy structure is difficult, which causes sharpening of theplateau slope or formation of two plateaus, leading to decrease in thecapacity and internal pressure characteristics of the batteries.

Thus development of hydrogen storage alloys is demanded in which theabove problems have been overcome, and which are easy to recycle, low incost, and excellent in corrosion resistance.

On the other hand, for improving the activity of hydrogen storage alloyswith expectation of improvement in battery activity, attempts have beenmade to treat the alloy surface with acid or alkali, or to increase theratio of the A-site components. However, the activity conflicts with thecorrosion resistance, and thus these methods for improving the activitysimultaneously impair the corrosion resistance.

In the art of metal hydride-hydrogen batteries, electrode activematerials that satisfy both of these conflicting properties have beenunder development, and as the materials for the active materials, amixture of an alloy excellent in corrosion resistance and an alloyexcellent in activity, has been proposed for use. However, the alloysexcellent in different properties used in this method are also differentin their compositions or structures, or obtained by totally differentproduction methods. Thus, even though the activity and the corrosionresistance are improved, the capacity and the internal pressurecharacteristics of the batteries are reduced, or the costs for recyclingthe batteries after use are increased.

SUMMARY OF THE INVENTION

It is therefor an object of the present invention to provide hydrogenstorage alloys, methods for producing the same, and anodes produced withsuch alloys for nickel-hydrogen rechargeable batteries, which alloys areuseful as electrode materials for nickel-hydrogen rechargeablebatteries, which are excellent, when used as anode materials, in bothcorrosion resistance and activity such as initial activity and high ratedischarge performance, which are of low cost compared to theconventional alloys with a higher Co content, and which are recyclable.

It is another object of the present invention to provide anodes fornickel-hydrogen rechargeable batteries in which the activity such asinitial activity and high rate discharge performance is well balancedwith the conflicting corrosion resistance, simply by using two or morekinds of particular hydrogen storage alloys of different crystal grainsizes.

In order to achieve these objects, the inventors of the presentinvention have made intensive studies in the relationship between thecomposition and structure of alloys and the corrosion resistance. As aresult of the studies, the inventors have found out that the aboveobjects may be achieved by limiting the B-site components within aparticular range, giving the alloy a single phase structure, and makingthe grain sizes of the crystals constituting the alloy structure fallwithin a particular range, as well as by producing anodes using two ormore kinds of hydrogen storage alloys of different crystal grain sizes.The present inventors have also made studies for methods for producingalloys that achieve the above objects, to complete methods forindustrially producing such alloys.

According to the present invention, there is provided a hydrogen storagealloy of a composition represented by the formula (1), wherein saidalloy has a substantially single phase structure, and crystals of saidalloy have an average long axis diameter of 30 to 160 μm:RNi_(x)Co_(y)M_(z)   (1)wherein R stands for one or a mixture of rare earth elements includingyttrium, M stands for Mg, Al, Mn, Fe, Cu, Zr, Ti, Mo, W, B, or mixturesthereof, x satisfies 3.75≦x≦5.3, y satisfies 0.1≦y≦0.5, z satisfies0.1≦z≦1.0, and 5.1≦x+y+z≦5.5 (referred to as alloy (a) hereinbelow).

According to the present invention, there is also provided a hydrogenstorage alloy of a composition represented by the formula (1), whereinsaid alloy has a substantially single phase structure, and crystals ofsaid alloy have an average long axis diameter of not smaller than 5 μmand smaller than 30 μm (referred to as alloy (b) hereinbelow).

According to the present invention, there is also provided a method forproducing alloy (a) comprising the steps of:

(A) melting materials for an alloy of a composition represented by theformula (1) to prepare an alloy melt;

(B-1) cooling and solidifying said alloy melt into alloy flakes havingan average thickness of 0.1 to 0.5 mm; and

(C-1) heat-treating said alloy flakes at 950 to 1100° C. for 30 minutesto 10 hours.

According to the present invention, there is further provided a methodfor producing alloy (b) comprising the steps of:

(A) melting materials for an alloy of a composition represented by theformula (1) to prepare an alloy melt;

(B-2) cooling and solidifying said alloy melt into alloy flakes havingan average thickness of 0.05 to 0.2 mm; and

(C-2) heat-treating said alloy flakes at 900 to 1000° C. for 1 to 10hours.

According to the present invention, there is also is provided an anodefor a nickel-hydrogen rechargeable battery comprising alloy (a) and anelectrically conductive material as anode materials.

According to the present invention, there is further provided an anodefor a nickel-hydrogen rechargeable battery comprising alloy (a), alloy(b), and an electrically conductive material as anode materials.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will now be explained in detail.

The alloys (a) and (b) of the present invention both have thecomposition represented by the formula (1). In the formula (1), R standsfor one or a mixture of two or more of rare earth elements includingyttrium. R may preferably be one or more elements selected from thegroup consisting mainly of La, Ce, Pr, and Nd for achieving improvedcorrosion resistance, when, for example, the alloy is used as an anodeactive material for a nickel-hydrogen rechargeable battery. It ispreferred to increase the La content in the composition of R forpreparing an active material of high capacity. The La content ispreferably not lower than 50%, more preferably not lower than 55%, mostpreferably not lower than 65%, by atomic percent. Accordingly, when R isone or more elements selected from the group consisting mainly of La,Ce, Pr, and Nd, it is preferred to suitably select the composition of Rfrom 50 to 100 at % La, 0 to 50 at % Ce, 0 to 50 at % Pr, and 0 to 50 at% of Nd.

In the formula (1), x and y denote the atomic ratios of Ni and Co,respectively. x representing the Ni content satisfies 3.7≦x≦5.3. As toy, the Co content is preferably as low as possible as long as thedesired corrosion resistance is achieved, since one of the objects ofthe present invention is to reduce the alloy cost by reducing the Cocontent. With the Co content y of over 0.5, the corrosion resistance isimproved, while the alloy cost is increased. With the Co content y ofless than 0.1, the corrosion resistance is inevitably lowered. Thus y is0.1≦y≦0.5, preferably 0.2≦y≦0.45.

In the formula (1), M represents additional elements for adjusting thehydrogen storage performance of the alloy, and stands for one or moreelements selected from the group consisting of Mg, Al, Mn, Fe, Cu, Zr,Ti, Mo, W, and B. When the alloy contains too large a number ofadditional elements, the inconveniences in recycling the alloy outstripthe contribution of the additional elements to the alloycharacteristics. Thus the number of additional elements is preferably 2to 5, more preferably 2 to 3. The content of M is denoted by z. With zof less than 0.1, the effect of the addition of the elements M on thealloy characteristics is too little, whereas even with z of over 1.0, nofurther increase in the effect is achieved, so that z is 0.1≦z≦1.0,preferably 0.35≦z≦1.0.

In the alloy of the present invention, the value of x+y+z representingthe ratio of the B-site elements is important. This value is one of thefactors for improving the corrosion resistance of the alloy. If thisvalue is less than 5.1, the corrosion resistance cannot be improved,whereas if more than 5.5, it is quite difficult to give the alloy asingle phase structure, and the corrosion resistance is lowered. Thusx+y+z is 5.1≦x+y+z≦5.5, preferably 5.2≦x+y+z≦5.4.

The structure of the present alloy is of a substantially single phasefor achieving the desired corrosion resistance. Whether an alloy is of asingle phase structure or not may be confirmed by X-ray diffraction orunder an electron microscope. Having a substantially single phasestructure herein means that the presence of other phases cannot beobserved clearly by these methods.

In the alloy (a) of the present invention, the average long axisdiameter of the crystal grains is 30 to 160 μm, preferably 30 to 120 μm,more preferably 70 to 100 μm, and it is particularly preferred that thecrystal grains are of a uniform size, for further improving thecorrosion resistance. With the average long axis diameter of less than30 μm, the desired corrosion resistance is hard to be achieved, whereaswith the average long axis diameter of over 160 μm, the activityrequired as an anode active material for a rechargeable battery cannotbe obtained.

In the alloy (b) of the present invention, the average long axisdiameter of the crystal grains is not smaller than 5 μm and smaller than30 μm, preferably not smaller than 10 μm and smaller than 30 μm, morepreferably 10-20 μm, and it is particularly preferred that the crystalgrains are of a uniform size for improving the activity when used incombination with the alloy (a) as anode active materials for arechargeable battery. With the average long axis diameter of smallerthan 5 μm, the desired corrosion resistance is hard to be achieved,whereas with the average long axis diameter of riot smaller than 30 μm,the activity as an anode active material for a rechargeable battery ishard to be improved in combination with the alloy (a).

The alloys of the present invention, when used for example as electrodematerials, maybe subjected to surface coating by plating or with a highpolymer, surface treatment with an acid or alkali solution, or anyconventional treatment, for the purpose of further improving variousproperties before the alloys are processed into electrodes.

The alloys of the present invention may be produced, for example, by themethods of the present invention including the steps of: (A) melting thematerials for an alloy of the composition represented by the formula (1)to prepare an alloy melt; (B-1) or (B-2) cooling and solidifying thealloy melt into alloy flakes having the particular average thickness;and (C-1) or (C-2) heat-treating the alloy flakes under the particularconditions. The melting step (A) may be performed in a conventionalmanner.

According to the methods of the present invention, the average long axisdiameter of the crystals of the resulting alloys may be regulated bycontrolling the cooling rate in preparing the alloy flakes, thethickness of the alloy flakes, and the like factors. In general, thehigher the cooling rate is, the smaller the long axis diameter of thecrystal grains is, and vice versa. In the methods of the presentinvention, since the alloys in the form of as-cast flakes do not have asingle phase structure, the alloy flakes are subsequently heat-treatedunder the particular conditions for giving a single phase structurethereto. If the cooling rate in the production of the alloy flakes istoo low, a secondary phase of crystals appear, which grow so coarse thatthe alloy flakes cannot be made into a single phase structure in thesubsequent heat treatment, thus not being preferred. On the other hand,if the cooling rate is too high, the crystals are made fine and readilymade into a single phase structure, but the thickness of the alloyflakes is hard to be controlled within the particular range, and theproductivity is lowered, thus not being preferred.

In view of the above, the cooling rate in producing the alloy flakes inthe methods of the present invention is usually in the range of 10 to3000° C. per second, preferably 100 to 1000° C. per second. The coolingrate may suitably be selected from the above range so that the alloyflakes have the particular thickness, taking the alloy composition andthickness of the alloy flakes into consideration.

In the method for producing alloy (a) of the present invention, if thealloy flakes are too thick, the radial temperature variation in thealloy flakes is great, which results in difficulty in generatingcrystals of a uniform size. Too thick alloy flakes also provide enlargedreaction areas, which cause too much growth of the crystals in thesubsequent long-time heat treatment. Thus, in step (B-1), the thicknessof the alloy flakes should be adjusted to 0.1 to 0.5 mm, preferably 0.2to 0.3 mm. Such alloy flakes may preferably be produced by single- ortwin-roll strip casting, centrifugal casting, or rotary disk casting.

On the other hand, in the method for producing alloy (b) of the presentinvention, since the average long axis diameter of the crystals of thealloy (b) is smaller than that of the alloy (a), the thickness of thealloy flakes should be adjusted to 0.05 to 0.2 mm in step (B-2).

In step (C-1) of the method for producing the alloy (a), the heattreatment for giving the alloy flakes a single phase structure isperformed at 950 to 1100° C. for 30 minutes to 10 hours. At lower than950° C., it takes too much time for the crystals to grow to thepredetermined crystal grain size, resulting in dispersion in the crystalgrain size. At higher than 1100° C., a secondary phase isreprecipitated, and the alloy of a single phase structure cannot beobtained.

In step (C-2) of the method for producing the alloy (b), the heattreatment for giving the alloy flakes a single phase structure isperformed at 900 to 1000° C. for 1 to 10 hours. At lower than 900° C.,the single phase structure is hard to be given to the alloy flakes, andit takes time for the crystals to grow to the predetermined crystalgrain size. At higher than 1000° C., the crystals may grow beyond thepredetermined grain size, or dispersion may occur in the crystal grainsizes.

The anode for a nickel-hydrogen rechargeable battery of the presentinvention contains the alloy (a), alloy (b) or a mixture of alloys (a)and (b), and an electrically conductive material, as anode materials.The alloy (a), alloy (b), or a mixture of alloys (a) and (b) acts as ananode active material in the rechargeable battery. The anode of thepresent invention may optionally contain other conventionally-usedcomponents, as long as the objects of the present invention is achieved,and may contain, in particular, other active materials.

The anode for a nickel-hydrogen rechargeable battery of the presentinvention may be produced using alloy (a) and/or alloy (b) as theessential components of the active material, which are mixed with abinder, an electrical conductivity assisting agent, and the like in aconventional manner, and molded into an anode. There is no particularlimitation imposed on the binder and the electrical conductivityassisting agent, and those used conventionally may be used here.

When the alloy (a) alone is used as the active material, the resultinganode exhibits excellent corrosion resistance, whereas when the alloy(b) alone is used as the active material, the resulting anode exhibitsexcellent initial activity and load characteristics. When the two alloysare used in combination, the resulting anode is given the properties ofthe both. For preparing an anode for a battery for general use havinginitial activity and corrosion resistance both improved, the mixingratio of the alloy (a) to the alloy (b) is preferably within a range of99:1 to 90:10 by weight. If the mixing ratio of the alloy (b) to thealloy (a) is too low, the initial activity cannot be improvedsufficiently, whereas if the mixing ratio of the alloy (b) is too high,the corrosion resistance cannot be improved sufficiently, thus not beingpreferred. For preparing an anode for a high-output power battery havinghigh rate discharge performance and corrosion resistance both improved,the mixing ratio of the alloy (a) to the alloy (b) is preferably withina range of 90:10 to 50:50. If the mixing ratio of the alloy (a) to thealloy (b) is too low, the corrosion resistance cannot be improvedsufficiently, whereas if the mixing ratio of the alloy (a) is too high,the high rate discharge performance cannot be improved sufficiently,thus not being preferred.

With the particular composition, substantially single phase structure,and controlled average long axis diameter of the crystals, the hydrogenstorage alloys of the present invention are useful as electrodematerials for nickel-hydrogen rechargeable batteries. When used as anodematerials, the present alloys exhibit excellent activities, such asinitial activity and high rate discharge performance, and excellentcorrosion resistance. The present alloys are also low in cost comparedto the conventional alloys with a higher Co content, and are recyclable.By the methods of the present invention, such hydrogen storage alloysare easily produced in an industrial scale.

Since the anodes for nickel-hydrogen rechargeable batteries of thepresent invention contain the hydrogen storage alloys of the presentinvention as the active materials, the advantages of the present alloyswhen used for anodes for rechargeable batteries mentioned above, areachieved. Further, nickel-hydrogen rechargeable batteries in which theactivity, in particular, the initial activity and the high ratedischarge performance, is well balanced with the conflicting corrosionresistance, may be provided simply by employing two or more ]kinds ofparticular hydrogen storage alloys having different crystal grain sizes.

EXAMPLES

The present invention will now be explained in more detail withreference to Examples and Comparative Examples, but the presentinvention is not limited thereto.

Examples 1-19 and Comparative Examples 1-3

Misch metal (abbreviated as Mm hereinbelow) manufactured by SantokuCorporation (rare earth composition: 70 at % La, 22 at % Ce, 2 at % Pr,and 6 at % Nd) Ni, Co, Mn, and Al were mixed at the elemental ratio of4.00:0.40:0.65:0.20, and subjected to high frequency induction meltingin an alumina crucible in an argon gas atmosphere to prepare an alloymelt. The alloy melt was rapidly cooled by single-roll strip casting toprepare alloy flakes of a hydrogen storage alloy having the averagethickness shown in Table 1. The obtained alloy flakes were heat-treatedin an argon gas atmosphere under the conditions shown in Table 1.

The resulting heat-treated hydrogen storage alloy was subjected toobservation of its alloy structure under a scanning electron microscope,and X-ray diffraction to see whether the alloy was substantially of asingle phase structure. Further, from the alloy structure observed undera scanning electron microscope, the average long axis diameter of thecrystal grains along the longitudinal axis of the alloy flakes wasdetermined. The results are shown in Table 1.

Next, the heat-treated alloy was mechanically pulverized to preparehydrogen storage alloy powders having the average particle size of notlarger than 60 μm. 1.2 g of the alloy powders were mixed with 1 g ofcarbonyl nickel as an electrically conductive material and 0.2 g offluororesin powders as a binder, and formed into fibers. The resultingfibers were wrapped with nickel mesh, and pressure molded under thepressure of 2.8 ton/cm² to thereby prepare an anode for anickel-hydrogen rechargeable battery. The obtained anode was placed in30% KOH, and subjected to a charge-discharge text in a pressure vesselunder 5 atm for evaluation of the initial activity, high rate dischargeperformance, and corrosion resistance.

The charge-discharge test was run for 10 cycles at the discharge currentof 0.2 C, and the ratio of the discharge capacity on the 3rd cycle tothe discharge capacity on the 10th cycle was taken as the initialactivity. The test was further run, and the capacity upon discharge at 1C on the 11th cycle was measured, and the ratio of this value to thedischarge capacity on the 10th cycle was taken as the high ratedischarge performance. The test was further run at the discharge currentof 0.2 C from the 12th cycle on, and the ratio of the capacitymaintained on the 600th cycle to the discharge capacity at the 10thcycle was taken as the corrosion resistance. The results are shown inTable 1. TABLE 1 Average Temperature Duration of Average Long Axis HighRate for Heat Heat Thickness of Diameter of Initial Discharge CorrosionTreatment Treatment Cast Pieces Single Phase/ Main Phase ActivityPerformance Resistance (° C.) (hrs) (mm) Secondary Phase (μm) (%) (%)(%) Example 1 950 0.5 0.230 Single phase 33 95.9 89.7 91.1 Example 2 9501 0.250 Single phase 62 94.3 86.9 94.8 Example 3 950 6 0.225 Singlephase 73 93.9 88.2 95.4 Example 4 950 10 0.396 Single phase 95 93.6 85.696.7 Example 5 1000 0.5 0.270 Single phase 52 95.6 87.0 95.7 Example 61000 1 0.220 Single phase 72 94.0 85.8 95.8 Example 7 1000 6 0.347Single phase 87 93.6 85.9 96.5 Example 8 1000 10 0.356 Single phase 8994.5 85.4 96.0 Example 9 1050 0.5 0.357 Single phase 106 93.4 85.7 96.1Example 10 1050 1 0.192 Single phase 74 94.2 86.0 96.6 Example 11 1050 60.203 Single phase 76 93.5 86.3 96.3 Example 12 1050 10 0.392 Singlephase 138 92.8 84.8 94.1 Example 13 1100 0.5 0.180 Single phase 53 95.188.7 93.0 Example 14 1100 1 0.272 Single phase 82 93.8 86.4 95.7 Example15 1100 6 0.400 Single phase 118 93.5 85.5 95.7 Example 16 1100 10 0.467Single phase 152 92.3 84.3 92.0 Example 17 900 10 0.163 Single phase 1398.3 93.7 83.6 Example 18 950 6 0.181 Single phase 17 97.4 91.3 85.1Example 19 1000 1 0.066 Single phase 15 97.7 92.2 84.6 Comp. Ex 1 850 100.146 Secondary phase 7.8 97.6 89.3 78.9 appeared Comp. Ex. 2 1200 50.289 Secondary phase 147 92.4 83.2 80.2 appeared Comp. Ex. 3 1000 100.593 Single phase 179 91.8 82.9 83.5

Examples 20-24 and Comparative Examples 4 and 5

Hydrogen storage alloys were prepared in the same manner and under thesame conditions as in Example 7, and subjected to each evaluation,except that the alloy compositions were as shown in Table 2. The resultsare shown in Table 2. TABLE 2 Corrosion La/ Ce/ Pr/ Nd/ Single Phase/Resistance Ni Co Al Mn AB_(x) TRE TRE TRE TRE Secondary Phase (%)Example 20 3.93 0.50 0.30 0.37 5.10 50 25 5 20 Single phase 95.2 Example21 4.15 0.20 0.40 0.45 5.20 60 40 0 0 Single phase 96.0 Example 22 4.150.40 0.30 0.45 5.30 72 21 2 6 Single phase 96.8 Example 23 4.10 0.300.43 0.57 5.40 83 12 1 4 Single phase 95.9 Example 24 4.35 0.10 0.400.65 5.50 100 0 0 0 Single phase 95.1 Comp. Ex. 4 3.75 0.40 0.25 0.605.00 60 23 3 14 Single phase 89.3 Comp. Ex. 5 4.35 0.30 0.50 0.45 5.6082 10 2 6 Secondary phase 86.8 appeared

Examples 25-33 and Comparative Examples 6-9

The hydrogen storage alloy prepared in Example 7 (referred to as alloy(a-1) hereinbelow) and the hydrogen storage alloy prepared in Example 18(referred to as alloy (b-1) hereinbelow) were mixed at the mixing ratioshown in Table 3, and an anode for a nickel-hydrogen rechargeablebattery was produced in the same manner as in Examples 1-19. Theresulting anode was subjected to each evaluation in the same manner asin Examples 1-19. The results are shown in Table 3.

A highly active alloy (c) having an equilibrium pressure 0.3 Mpa higherthan that of alloy (a-1), was prepared through the melting, casting, andheat-treating steps in the same manner as in Example 7, except that theelemental ratio of the alloy was Mm:Ni:Co:Al:Mn=1:3.55:0.80:0.25:0.37(Rare earth (Mm) composition: 41 wt % La, 43 wt % Ce, 4 wt % Pr, and 12wt % Nd). The alloy (a-1) and alloy (c) were mixed at the mixing ratioof 50:50, and an anode for a nickel-hydrogen rechargeable battery wasproduced in the same manner as in Examples 1-19. The resulting anode wassubjected to each evaluation in the same manner as in Examples 1-19. Theresults are shown in Table 3. TABLE 3 High Rate Initial DischargeCorrosion Alloy Alloy Alloy Activity Performance Resistance (a-1) (b-1)(c) (%) (%) (%) Example 25 99 1 0 95.8 90.2 96.3 Example 26 95 5 0 96.490.8 96.2 Example 27 90 10 0 97.1 91.2 96.0 Example 28 80 20 0 97.6 91.794.7 Example 29 70 30 0 98.0 92.0 94.0 Example 30 50 50 0 98.1 92.6 92.6Comp. Ex. 6 100 0 0 93.6 85.9 96.5 Comp. Ex. 7 40 60 0 98.1 92.9 91.3Comp. Ex. 8 20 80 0 98.2 93.2 89.8 Comp. Ex. 9 0 100 0 98.3 93.7 83.6Comp. Ex. 10 50 0 50 92.3 90.8 86.2

1-6. (canceled)
 7. A method for producing an alloy of claim 10comprising the steps of: (A) melting materials for all alloy of acomposition represented by the Formula (1) to prepare an alloy melt;(B-1) cooling and solidifying said alloy melt into alloy flakes havingan average thickness of 0.1 to 0.5 mm; and (C-1) heat-treating saidalloy flakes at 950 to 1100° C. for 30 minutes to 10 hours.
 8. A methodfor producing am alloy of claim 10 comprising the steps of: (A) meltingmaterials for an alloy of a composition represented by the formula (1)to prepare an alloy melt; (B-2) cooling and solidifying said alloy meltinto alloy flakes having all average thickness of 0.05 to 0.2 mm; and(C-1) heat-treating said alloy flakes at 900 to 1000° C. for 30 minutesto 10 hours.
 9. canceled
 10. An anode for a nickel-hydrogen rechargeablebattery comprising, as anode materials: a hydrogen storage alloy (a), acomposition represented by the formula (1), wherein said alloy has asubstantially single phase structure, and crystals of said alloy have anaverage long axis diameter of 30 to 160 μm;RNi_(x)Co_(y)M_(z)   (1) wherein R stands for once or a mixture of rareearth elements including yttrium, M stands for Mg, Al, Mn, Fe, Cu, Zr,Ti, Mo, W, B, or mixtures thereof, x satisfies 3.7≦x≦5.3, y satisfies0.1≦x≦0.5, satisfies 0.1≦x≦1.0, and 5.1≦x=Y=z≦5.5, a hydrogen storagealloy (b), a composition represented by the formula (1), wherein saidalloy has a substantially single phase structure, and crystals of saidalloy have an average long axis diameter of not smaller than 5 μm andsmaller than 30 μm, and an electrically conductive material.
 11. Theanode for a nickel-hydrogen rechargeable battery of claim 10, wherein aratio of said hydrogen storage alloy (a) to said hydrogen storage alloy(b) existing in said anode materials is 99:1 to 90:10.
 12. The anode fora nickel-hydrogen rechargeable battery of claim 10 wherein said R in theformula (1) for said alloys (a) and (b) is selected from the groupconsisting of La, Ce, Pr, Nd and mixtures thereof.
 13. The anode for anickel-hydrogen rechargeable battery of claim 12, wherein a compositionof said R in the formula (1) for said alloys (a) and (b) is 50 to 100 at% Ce, 0 to 50 at % Pr, and 0 to 50 at % Nd.
 14. The anode for anickel-hydrogen rechargeable battery of claim 10, wherein said averagelong axis diameter of crystals of said alloy (a) is 30 to 120 μm. 15.The anode for a nickel-hydrogen rechargeable battery of claim 10,wherein said average long axis diameter of crystals of said alloy (b) is10 to 20 μm.